The residue from petroleum distillation has a wide number of uses, including paving asphalt and fuel. Paving grade asphalt used in road construction must meet a number of specifications, including the latest SHRP specification, viscosity (usually 200-5000 poises at 60.degree. F.), penetration (usually greater than 30 to 200 dmm), penetration ratio 15.degree. F./25.degree. F. (usually above about 0.3), ductility, temperature susceptibility, and others.
Contacting the resid fraction of petroleum with air at an elevated temperature, also referred to as "air blowing," is a conventional way to improve the characteristics of certain grades of resid to make them suitable for use as a paving asphalt. However, the prior art does not appear to disclose the practical application of air blowing a relatively soft resid to obtain a relatively hard resid that can be pelletized for storage and/or shipment. As used in the present specification and claims, a "soft resid" or a "low softening point temperature" refers to a petroleum residue having a penetration above 0 and Ring and Ball (R&B) softening point temperature below 200.degree. F. A "hard resid" or a "high softening point temperature" refers to a petroleum residue with a penetration of essentially 0 and R&B softening point temperature above 200.degree. F.
Representative references disclosing resid or asphaltene air blowing equipment and methodology include U.S. Pat. No. 2,616,837 to Roediger; U.S. Pat. No. 2,627,498 to Fink et al; U.S. Pat. No. 2,861,939 to Biribauer et al; U.S. Pat. No. 2,889,296 to Morris et al; U.S. Pat. No. 3,462,359 to Fauber; U.S. Pat. No. 3,598,716 to Fauber; U.S. Pat. No. 3,751,278 to Alexander; U.S. Pat. No. 3,779,892 to Forster et al; U.S. Pat. No. 3,868,315 to Forster et al; U.S. Pat. No. 3,935,093 to Senolt et al; U.S. Pat. No. 3,989,616 to Pagen et al; U.S. Pat. No. 4,052,290 to Cushman et al; U.S. Pat. No. 4,207,117 to Espenscheid et al; U.S. Pat. No. 4,283,230 to Clementoni et al; U.S Pat. No. 4,332,671 to Boyer; U.S. Pat. No. 4,933,067 to Rankel; U.S. Pat. No. 4,975,176 to Begliardi et al; U.S. Pat. No. 5,228,977 to Moran et al; U.S. Pat. No. 5,320,739 to Moran et al; U.S. Pat. No. 5,932,186 to Romine et al; and U.S. Pat. No. 5,939,474 to Gooswilligen et al. Air blowing technology is commercially available under the trade designation BITUROX, for example.
In contrast to paving asphalt, the specifications for fuel grade petroleum resid that is burned as a fuel are much less stringent. The resid generally has a higher calorific value and better combustion characteristics compared to coal and petroleum coke, which is why resid has been added to coal and coke as fuel additive to aid combustion. However, heavy resid with a low softening point temperature is difficult to store and/or transport without significant handling and packaging requirements. Over time, even when they initially may appear to be solid at ambient conditions, these low-softening-point-materials exhibit liquid flow characteristics at elevated temperatures. These materials have typically been transported as a semi-solid product, as a neat liquid product, or as a cutback liquid product. The semi-solid form must be shipped in a closed container to prevent leakage and spillage, is usually reheated prior to use, and the high cost of packaging and handling the material in this manner usually limits application to relatively small volumes of product.
As a neat liquid product, heavy resid is maintained at elevated temperatures sufficient to keep the material in a liquid state. This method is also expensive and has limited practical application.
As a cutback liquid product, heavy resid is mixed with light hydrocarbon cutterstocks to maintain the mixture in a liquid state at lower temperatures. As a result, the lighter hydrocarbons with which the resid is blended are substantially downgraded in value.
A pelletized resid that remains solid would be free flowing and could be readily stored, packaged, transported and handled. Previous attempts at pelletizing resid with a low softening point temperature have relied on encapsulating the resid with a solid coating. Coating the resid complicates the encapsulating process, results in a compositionally heterogeneous product, adds cost due to the generally expensive nature of the coating material, is not always effective due to rupture or breakage of the coating and/or to dissolution of the coating by water if the coating is water soluble, and the coating can adversely affect the combustion characteristics of the resid. Representative references teaching various encapsulation apparatus and methodology include U.S. Pat. No. 3,015,128 to Somerville; U.S. Pat. No. 3,310,612 to Somerville; U.S. Pat. No. 4,123,206 to Dannelly; U.S. Pat. No. 4,128,409 to Dannelly; U.S. Pat. No. 4,386,895 to Sodickson; and U.S. Pat. No. 5,637,350 to Ross.
U.S. Pat. No. 4,931,231 to Teppo et al discloses a method for manufacturing discrete pellets of asphaltic material by flowing the asphaltic material in molten form as an elongated annular stream directly into cooling water to solidify and shatter the elongated stream into discrete solid particles. The particles formed as a result of shattering are not spherical and have undesirable flow and/or handling characteristics. For example, the particles may be dust-free when made, but because of any jagged edges, might result in formation of considerable dust upon handling.
U.S. Pat. No. 3,877,918 to Cerbo discloses apparatus for producing spherical glass particles by centrifugally projecting solid crushed glass particles into the draft tube of a bead furnace using a rotary receptacle. The rotary receptacle forms a cloud of evenly dispersed solid glass particles, which are directed upwardly into the expansion chamber of the furnace to heat and shape the glass particles by surface tension into spheres.
The prior art does not appear to disclose a method or apparatus for making spherical petroleum resid pellets by feeding the resid in a molten state to a rotating prilling head, allowing the resid discharged from the prilling head to break into particles and form into spheres due to the surface tension of the molten resid as the particles pass by gravity through a high temperature zone, and then quenching the molten material in a cooling medium to solidify the particles in their substantially spherical form. Nor does there appear to be any prior disclosure of substantially spherical, compositionally homogeneous (uncoated) petroleum resid pellets having a high softening point temperature, nor of a method or apparatus for making spherical resid pellets for ambient temperature storage and shipment for use in combustion processes as a fuel or fuel additive.